The invention is directed to a process for the production and recovery of chemicals, in particular hydrocarbons, from a fermentation medium.
Production of hydrocarbon starting materials by fermentation is an alternative to production from petroleum. Fermentation uses renewable resources and creates much less hazardous waste. The fermentative production of a few chemicals has been reported. Unfortunately, this is not a commercially feasible alternative for a great many desirable compounds because the compound of interest is produced in small amounts by the biocatalytic organisms. Even organisms that are genetically engineered to produce enhanced amounts of the desired compound often do not produce concentrations of the product high enough to justify the investments necessary to develop a commercial biofermentation process. This can be particularly true when the product is toxic to the cells or is regulated by a negative feedback mechanism, thereby limiting the potential concentration of the product in the fermentation medium.
WO-A-00/18942 describes a process wherein 4-hydroxybenzoic acid (PHB) is produced by fermentation. According to this process, the product PHB is removed from the fermentation during at least a portion of the fermentation by passing the fermentation medium through an anion exchange resin which binds PHB. Subsequently the anion exchange resin is extracted to remove bound PHB. Although this known process is said to result in improvements in recovery of the product and higher production of the product by the biocatalyst, there remain a number of disadvantages. First, the ion exchange resin needs to be applied in the form of a packed bed, which may result in considerable pressure drop and fouling of the bed. Moreover, ion exchange resins may have a negative influence on the biocatalyst (i.e., the microorganisms), since these resins can be poisonous to these biocatalysts. It is also possible that these resins bind essential nutrients for the biocatalyst. Also ion exchange resin particles are susceptible to biofouling. For these and other reasons, the extraction of product from the medium is carried out by contacting the medium in-stream (viz. outside the fermentor) with the resin, so that contact between resin and biocatalyst is minimized. Furthermore, because of fouling (viz. attachment of biocatalyst to the resin surface, resulting in decreased sorption capacity of the resin) of the resin, amongst others, it is not possible to carry out this process in a continuous fashion. For these reasons, the product yield of the process of WO-A-00/18942, like the product yield of other known processes, is limited.
Furthermore, WO-A-00/73485 describes a process for the extraction of a fermentation product from a broth, using a solvent that is encapsulated in a membrane. However, this process, as well as other membrane based processes for the recovery of products from fermentation processes, are hampered by slow absorption kinetics, as a result of the mass transfer barrier posed by the membrane. In addition, regeneration of these capsule absorbentia is generally difficult. Furthermore, the preparation of the encapsulated solvent is cumbersome.
Alternatively, liquid-liquid extraction by directly contacting the broth with a solvent for the product generally is also not an option, since this generally does not result in the desired suspended droplets of solvents which subsequently coalesce so that they could be separated by gravity, but rather this leads to the formation of an emulsion. These emulsions may be very stable and consequently it is very difficult or impossible to obtain the product from the solvent.
It is an object of the present invention to provide a process for the production of hydrocarbons, such as 4-hydroxybenzoic acid and benzaldehyde, which process, at least in part, overcomes the above-mentioned disadvantages. Other examples of hydrocarbons that may be produced according to the present invention are catechols (e.g. 3-methylcatechol), benzylalcohol, cinnamic acid, as well as mixtures of these and other hydrocarbons. In general, each compound (of commercial value) that can be extracted using a suitable solvent.
It has been found that by using solvent impregnated porous carrier particles, which particles may either float or sink in the broth, to perform the separation of the product from the broth in the fermentation process, this object can be met.